Heat registers for forced air heating systems have been used for a long time. Today's heat registers are typically rectangular. They have a top plate that has a set of formed louvers. A lower rectangular box is attached to install the register in a floor. A set of rotatable dampers is installed in the box to control the amount of air through the register. Most registers are built of lightweight metal or plastic and are welded, or riveted together or formed by injection molding. Virtually all household registers have fixed louvers formed in the cover.
There are air handling louver systems that have movable louvers. These tend to be larger industrial models. Some of these designs use bi-metallic strips to operate the louvers. In cold weather, for example, the louvers are closed. As the temperature increases, the bi-metallic strip causes the louvers to open, thereby increasing ventilation. Some examples of these louver systems are found in U.S. Pat. No. 2,698,570 to Feinberg, U.S. Pat. No. 2,117,529 to Wile et al., and U.S. Pat. No. 3,068,776 to Day. As noted above, these designs are large and have simple mechanisms that open and close the louvers as a unit.